A torque converter for an automatic transmission may include a torque converter clutch. When an engine output and a transmission input are operating at the same rotational speed, the torque converter clutch may be engaged to mechanically couple an impeller of the torque converter to a turbine of the torque converter to reduce energy losses associated with the fluid coupling provided by the torque converter. During some driving conditions, it is advantageous to allow a certain amount of clutch slip across the torque converter clutch, so that the impeller and the turbine may have a pre-defined amount of relative rotation therebetween.
The amount of torque converter clutch slip varies with different driving conditions. A transmission control module includes a torque converter clutch slip calibration table, which defines the desired amount of clutch slip for the current driving conditions. The transmission control module measures or senses different variables related to the current driving conditions, and uses those measured data points as inputs to select the desired clutch slip from the torque converter clutch slip calibration table. The values of the clutch slip are pre-defined, and stored in the torque converter clutch slip calibration table, in the memory of the transmission control module.
The different values for the amount of clutch slip for the different driving conditions must be defined to maintain an interface temperature of the friction surfaces of the torque converter clutch below a threshold temperature level. It is important to maintain the interface temperature of the torque converter clutch, i.e., the temperature between the friction surfaces of the torque converter clutch, to temperatures below the threshold temperature value, to prevent overheating and degradation of the transmission fluid.